fix: correct y axis title in boxplot when mark.extent isnt set (#9483)

src/compositemark/boxplot.ts

@@ -9,7 +9,7 @@ import {MarkInvalidMixins} from '../invalid';
 import {NormalizerParams} from '../normalize';
 import {GenericUnitSpec, NormalizedLayerSpec, NormalizedUnitSpec} from '../spec';
 import {AggregatedFieldDef, CalculateTransform, JoinAggregateTransform, Transform} from '../transform';
-import {accessWithDatumToUnescapedPath, isEmpty, omit, removePathFromField} from '../util';
+import {accessWithDatumToUnescapedPath, removePathFromField} from '../util';
 import {CompositeMarkNormalizer} from './base';
 import {
   compositeMarkContinuousAxis,
@@ -301,7 +301,6 @@ export function normalizeBoxPlot(
 
   const {scale, axis} = continuousAxisChannelDef;
   const title = getTitle(continuousAxisChannelDef);
-  const axisWithoutTitle = omit(axis, ['title']);
 
   const outlierLayersMixins = partLayerMixins<BoxPlotPartsMixins>(markDef, 'outliers', config.boxplot, {
     transform: [{filter: `(${fieldExpr} < ${lowerWhiskerExpr}) || (${fieldExpr} > ${upperWhiskerExpr})`}],
@@ -312,8 +311,7 @@ export function normalizeBoxPlot(
         type: continuousAxisChannelDef.type,
         ...(title !== undefined ? {title} : {}),
         ...(scale !== undefined ? {scale} : {}),
-        // add axis without title since we already added the title above
-        ...(isEmpty(axisWithoutTitle) ? {} : {axis: axisWithoutTitle})
+        ...(axis !== undefined ? {axis} : {})
       },
       ...encodingWithoutSizeColorContinuousAxisAndTooltip,
       ...(color ? {color} : {}),

test/compositemark/boxplot.test.ts

@@ -1166,4 +1166,27 @@ describe('normalizeBoxIQR', () => {
       as: `${timeUnit}_${field}`
     });
   });
+
+  it('should produce correct y axis title when mark.extent is not explicitly set', () => {
+    const normalizedSpec = normalize(
+      {
+        data: {url: 'data/population.json'},
+        mark: {
+          type: 'boxplot'
+        },
+        encoding: {
+          x: {field: 'age', type: 'quantitative'},
+          y: {
+            field: 'people',
+            type: 'quantitative',
+            axis: {title: 'Population'}
+          },
+          color: {value: 'skyblue'}
+        }
+      },
+      defaultConfig
+    );
+    const title = (normalizedSpec as any).layer[0].layer[0].encoding.y.axis.title;
+    expect(title).toBe('Population');
+  });
 });